Update chapter2.tex

Added parenthesis and a step clarifying the computation.

Author: pabloocal

Chapters/chapter2.tex

@@ -583,7 +583,8 @@ \subsection{Projections and Unit Vectors}
 compute $s$, we use the fact that the vector ${\rm proj}_\bb\aa - \aa$
 (along the dotted line in the diagram) is orthogonal to $\bb$. Thus
 $({\rm proj}_\bb\aa - \aa)\cdot\bb = 0$, or $(s\bb-\aa)\cdot\bb=0$, or
-$s = \aa\cdot\bb / \bb\cdot\bb = \aa\cdot\bb / \|\bb\|^2$. Thus
+$(s\bb)\cdot\bb-\aa\cdot\bb=0$, or $s(\bb\cdot\bb)=\aa\cdot\bb=$, or
+$s = (\aa\cdot\bb) / (\bb\cdot\bb) = (\aa\cdot\bb) / \|\bb\|^2$. Thus
 \begin{equation}
 \label{eq:projection}
 {\rm proj}_\bb\aa = {{\aa\cdot\bb}\over{\|\bb\|^2}}\bb.